ericatcw writes: JavaScript, so ubiquitous on today's AJAX-heavy Web sites, can slows down most popular sites today, says a Google performance guru. Steve Souders, the creator of the popular, free Yslow diagnostic tool, says that too many sites load too many JavaScript files at the beginning, creating a bottleneck, since browsers can't render or download anything else at the same time. New browsers such as Internet Explorer 8 can do "parallel downloads" of JavaScript, but it only partly solves the problem, says Souders, who calls for JavaScript and CSS files to be rewritten.